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><H1
><A
NAME="SQL-CREATEFOREIGNDATAWRAPPER"
></A
>CREATE FOREIGN DATA WRAPPER</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN65136"
></A
><H2
>Name</H2
>CREATE FOREIGN DATA WRAPPER&nbsp;--&nbsp;define a new foreign-data wrapper</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN65141"
></A
><H2
>Synopsis</H2
><PRE
CLASS="SYNOPSIS"
>CREATE FOREIGN DATA WRAPPER <TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
>
    [ HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
> | NO HANDLER ]
    [ VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
> | NO VALIDATOR ]
    [ OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] ) ]</PRE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65148"
></A
><H2
>Description</H2
><P
>   <TT
CLASS="COMMAND"
>CREATE FOREIGN DATA WRAPPER</TT
> creates a new
   foreign-data wrapper.  The user who defines a foreign-data wrapper
   becomes its owner.
  </P
><P
>   The foreign-data wrapper name must be unique within the database.
  </P
><P
>   Only superusers can create foreign-data wrappers.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65154"
></A
><H2
>Parameters</H2
><P
></P
><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="REPLACEABLE"
><I
>name</I
></TT
></DT
><DD
><P
>      The name of the foreign-data wrapper to be created.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>HANDLER <TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>handler_function</I
></TT
> is the
      name of a previously registered function that will be called to
      retrieve the execution functions for foreign tables.
      The handler function must take no arguments, and
      its return type must be <TT
CLASS="TYPE"
>fdw_handler</TT
>.
     </P
><P
>      It is possible to create a foreign-data wrapper with no handler
      function, but foreign tables using such a wrapper can only be declared,
      not accessed.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>VALIDATOR <TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
></TT
></DT
><DD
><P
><TT
CLASS="REPLACEABLE"
><I
>validator_function</I
></TT
> is the
      name of a previously registered function that will be called to
      check the generic options given to the foreign-data wrapper, as
      well as options for foreign servers and user mappings using the
      foreign-data wrapper.  If no validator function or <TT
CLASS="LITERAL"
>NO
      VALIDATOR</TT
> is specified, then options will not be
      checked at creation time.  (Foreign-data wrappers will possibly
      ignore or reject invalid option specifications at run time,
      depending on the implementation.)  The validator function must
      take two arguments: one of type <TT
CLASS="TYPE"
>text[]</TT
>, which will
      contain the array of options as stored in the system catalogs,
      and one of type <TT
CLASS="TYPE"
>oid</TT
>, which will be the OID of the
      system catalog containing the options. The return type is ignored;
      the function should report invalid options using the
      <CODE
CLASS="FUNCTION"
>ereport(ERROR)</CODE
> function.
     </P
></DD
><DT
><TT
CLASS="LITERAL"
>OPTIONS ( <TT
CLASS="REPLACEABLE"
><I
>option</I
></TT
> '<TT
CLASS="REPLACEABLE"
><I
>value</I
></TT
>' [, ... ] )</TT
></DT
><DD
><P
>      This clause specifies options for the new foreign-data wrapper.
      The allowed option names and values are specific to each foreign
      data wrapper and are validated using the foreign-data wrapper's
      validator function.  Option names must be unique.
     </P
></DD
></DL
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65189"
></A
><H2
>Notes</H2
><P
>   At the moment, the foreign-data wrapper functionality is rudimentary.
   There is no support for updating a foreign table, and optimization of
   queries is primitive (and mostly left to the wrapper, too).
  </P
><P
>   There is one built-in foreign-data wrapper validator function
   provided:
   <TT
CLASS="FILENAME"
>postgresql_fdw_validator</TT
>, which accepts
   options corresponding to <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> connection
   parameters.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65195"
></A
><H2
>Examples</H2
><P
>   Create a useless foreign-data wrapper <TT
CLASS="LITERAL"
>dummy</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER dummy;</PRE
><P>
  </P
><P
>   Create a foreign-data wrapper <TT
CLASS="LITERAL"
>file</TT
> with
   handler function <TT
CLASS="LITERAL"
>file_fdw_handler</TT
>:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER file HANDLER file_fdw_handler;</PRE
><P>
  </P
><P
>   Create a foreign-data wrapper <TT
CLASS="LITERAL"
>mywrapper</TT
> with some
   options:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE FOREIGN DATA WRAPPER mywrapper
    OPTIONS (debug 'true');</PRE
><P></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65207"
></A
><H2
>Compatibility</H2
><P
>   <TT
CLASS="COMMAND"
>CREATE FOREIGN DATA WRAPPER</TT
> conforms to ISO/IEC
   9075-9 (SQL/MED), with the exception that the <TT
CLASS="LITERAL"
>HANDLER</TT
>
   and <TT
CLASS="LITERAL"
>VALIDATOR</TT
> clauses are extensions and the standard
   clauses <TT
CLASS="LITERAL"
>LIBRARY</TT
> and <TT
CLASS="LITERAL"
>LANGUAGE</TT
>
   are not implemented in PostgreSQL.
  </P
><P
>   Note, however, that the SQL/MED functionality as a whole is not yet
   conforming.
  </P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN65216"
></A
><H2
>See Also</H2
><A
HREF="sql-alterforeigndatawrapper.html"
>ALTER FOREIGN DATA WRAPPER</A
>, <A
HREF="sql-dropforeigndatawrapper.html"
>DROP FOREIGN DATA WRAPPER</A
>, <A
HREF="sql-createserver.html"
>CREATE SERVER</A
>, <A
HREF="sql-createusermapping.html"
>CREATE USER MAPPING</A
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